The Australian held town of Port Moresby, on the southeastern coast of Papua New Guinea, was the last major airfield between the expanded Japanese territory and the Australian continent. In late May 1942, the Australian garrison there remained inadequate and the Japanese were resolved to take it before it could be reinforced. However in the first strategic setback for Japanese arms, their invasion fleet was broken up and forced to turn back by American and Australian naval forces in the Battle of the Coral Sea. Undeterred, the Japanese tried marching through the jungles of New Guinea to Port Morebsy instead. In a long, drawn out battle of attrition in the worst possible conditions on the Kokoda Trail northeast of Port Moresby, the Australian army managed to be the first western troops to defeat the Imperial Japanese Army.
Concerned that the initiative was passing to the Allies, the Japanese navy conceived of an attack in a different direction, towards the American outpost on Midway Island in the Pacific. Allied codebreakers were able to warn the admirals of the coming attack, and the remaining US carriers ambushed the Japanese in the Battle of Midway, inflicting a decisive defeat on the cream of the Japanese navy. With the loss of so many carriers and experienced naval aviators, further advances by the Japanese were out of the question.
